This invention relates generally to inkjet printers/plotters, and more specifically to carriage-mounted optical sensors in an inkjet printer/plotter.
Many print quality benefits are achieved by mounting an optical sensor on a carriage which also carries printing elements, since the optical sensor can then pass over the media upon which the printing elements are applying alphanumeric indicia, graphics or images. For example, see commonly assigned U.S. Pat. No. 5,170,047, entitled OPTICAL SENSOR FOR PLOTTER PEN VERIFICATION, and U.S. Pat. No. 5,448,269 entitled MULTIPLE INKJET CARTRIDGE ALIGNMENT FOR BIDIRECTIONAL PRINTING BY SCANNING A REFERENCE PATTERN, both of which are incorporated herein by reference.
The full color inkjet printer/plotters which have been developed comprise a plurality of inkjet pens of diverse colors. A typical color inkjet printer/plotter has four inkjet pens, one that stores black ink, and three that store colored inks, e.g., magenta, cyan and yellow. The colors from the three color pens are mixed to obtain any particular color.
The pens are typically mounted in stalls within an assembly which is mounted on the carriage of the printer/plotter. The carriage assembly positions the inkjet pens and typically holds the circuitry required for interface to the heater circuits in the inkjet pens.
Full color printing and plotting requires that the colors from the individual pens be precisely applies to the media. This requires precise alignment of the carriage assembly. Unfortunately, mechanical misalignment of the pens in conventional inkjet printer/plotters results in offsets in the X direction (in the media or paper axis) and in the Y direction (in the scan or carriage axis). This misalignment of the carriage assembly manifests as a misregistration of the print images applied by the individual pens. In addition, other misalignments may arise due to the speed of the carriage, the curvature of the platen and/or spray from the nozzles.
However, the integration of the optical and electronic components in the optical sensor, as well as positioning the optical sensor on the carriage have been complicated, expensive and to some extent imprecise in prior printers/plotters. The need for reliability and precision is even greater in recent inkjet printers/plotters which print high resolution color graphics and images, often on very large poster-size printouts.